CN113200761B - Preparation method of alumina porous ceramic with similar ceramic fiber net structure inside - Google Patents

Preparation method of alumina porous ceramic with similar ceramic fiber net structure inside Download PDF

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CN113200761B
CN113200761B CN202110673848.0A CN202110673848A CN113200761B CN 113200761 B CN113200761 B CN 113200761B CN 202110673848 A CN202110673848 A CN 202110673848A CN 113200761 B CN113200761 B CN 113200761B
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porous ceramic
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CN113200761A (en
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胡春峰
邬竣韬
陈宏宇
罗茜
萨尔瓦托·格拉索
冯庆国
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Southwest Jiaotong University
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Abstract

The invention discloses a preparation method of alumina porous ceramic with an internal structure similar to a ceramic fiber net structure, and relates to the technical field of ceramic preparation; the method comprises the following steps: (1) the organic slurry of the alumina whisker and the nano-scale alumina powder at least comprises the following components in a weight ratio of 1:1 or according to any proportion within the range of 1 to 6, uniformly mixing with 70ml of deionized water to form suspension; (2) transferring the suspension obtained in the step (1) into a suction filtration device, and performing suction filtration on water by using a vacuum pump to obtain a ceramic wet blank; (3) drying the wet blank obtained in the step (2) to obtain a biscuit; (4) and (4) sintering the biscuit obtained in the step (3) at the highest sintering temperature of 1200-1400 ℃ to obtain the porous ceramic. The preparation method has the advantages of simple preparation process, low cost and easy industrial popularization, and the prepared alumina porous ceramic has the characteristics of higher mechanical strength and higher porosity, so that the alumina porous ceramic has wide application prospects in the aspects of high-temperature heat preservation and high-temperature gas filtration.

Description

Preparation method of alumina porous ceramic with similar ceramic fiber net structure inside
Technical Field
The invention relates to a preparation method of porous ceramic, in particular to Al 2 O 3 A preparation method of porous ceramics.
Background
α-Al 2 O 3 Is all of Al 2 O 3 The most stable phase, whose stability derives from its crystal structure. Alumina is A 2 B 3 type-A compound, alpha-Al 2 O 3 Belonging to a trigonal system, oxygen atoms in the structure are approximately close-packed in a hexagonal shape, and aluminum atoms are filled in octahedral gaps therein. Because the crystal structure is composed of 3 oxygen atomsThe resultant surface is common to two adjacent octahedra, and the structure is such that alpha-Al 2 O 3 Has strong stability. While alpha-Al 2 O 3 Is also a common ceramic raw material. alpha-Al 2 O 3 The ceramic has the characteristics of excellent mechanical strength, thermal stability, electrical insulation and the like.
α-Al 2 O 3 Can be prepared into porous ceramics which can be widely applied to the fields of chemical industry, environmental protection, fire safety, biological medicine and the like as a filler, a building material, a filter and a catalyst carrier. The mature preparation process of porous ceramics, such as a pore-forming agent adding process, a foaming process and the like, mostly creates holes in a ceramic solid blank by some means to obtain the porous ceramics, but cannot form a fluffy structure similar to a ceramic fiber membrane with high porosity and ultrafine holes on a microcosmic scale. In International ceramics, volume 45 and volume 4 of 2019, it was pointed out that the preparation of porous ceramics using whiskers has a wide scope of research in the field of material science, but porous Al is prepared directly from single crystal alumina whiskers by suction filtration molding 2 O 3 Studies of ceramics have been rarely reported. In view of the fact that alumina is stable in chemical properties and difficult to sinter at a low temperature to form a reliable mechanical structure, further research and discussion can be made on the aspect of the nano sintering aid applicable to such porous materials in the future, and the mechanical strength of the material is increased while the high porosity of the material is maintained to be more than 80%.
Although there are review articles which describe Al prepared by the SPS process 2 O 3 The whisker reinforced alumina ceramic is a research object, and the influence of the addition amount of the whisker on the sintering behavior and the room temperature mechanical property is mainly researched. However, the ceramics prepared were fully dense and the whiskers degraded severely, with insufficient voids present. Therefore, how to prepare the porous ceramic material with both mechanical strength and high porosity by a simple process at a lower cost still remains a problem to be solved urgently.
Disclosure of Invention
The invention discloses a preparation method of alumina porous ceramic with an internal structure similar to a ceramic fiber net structure, which has low cost and simple process.
In order to achieve the object, the preparation technology adopted by the invention comprises the following steps:
(1)α-Al 2 O 3 whiskers and nanoscale alpha-Al 2 O 3 The organic matter slurry of the powder is at least mixed according to the weight ratio of 1:1 or according to any proportion within the range of 1 to 6 in weight ratio, uniformly mixing with 70ml of deionized water to form suspension;
(2) transferring the suspension obtained in the step (1) into a suction filtration device, and performing suction filtration on water by using a vacuum pump to obtain a ceramic wet blank;
(3) drying the wet blank obtained in the step (2) to obtain a biscuit;
(4) and (4) sintering the biscuit obtained in the step (3) at the highest sintering temperature of 1200-1400 ℃ to obtain the porous ceramic.
Further, the average diameter of the alumina whiskers in the step (1) is 0.6 μm, and the average length is 9.2 μm; the inherent content of the alumina organic slurry was 76%.
Further, the mixing process of the suspension obtained in the step (1) further comprises the following steps:
mixing the alumina whisker and 70ml of deionized water, putting the mixture into an ultrasonic dispersion machine for ultrasonic mixing, and taking out the mixture after the mixture is fully dispersed until no whisker visible to naked eyes is agglomerated to obtain a turbid liquid. And (3) adding the alumina organic matter slurry into the suspension, transferring the suspension into a planetary ball mill, and carrying out ball milling and stirring to obtain the suspension in the step (1), and finally obtaining uniform suspension.
Further, the vacuumizing pressure of the vacuum pump in the step (2) is 100 mbar.
Further, a small amount of silicone grease is coated on the inner wall of the suction filtration device in the step (2).
Further, the drying process in the step (3) is drying for 24 hours at a constant temperature of 40 ℃ by using a drying oven.
Further, in the sintering process in the step (4), the heating rate is 5 ℃/min.
Further, in the sintering process in the step (4), the heat preservation time at the sintering temperature is 360 min.
Further, in the cooling process in the step (4), the cooling rate is 5 ℃/min, and the furnace temperature is cooled along with the furnace after being reduced to 300 ℃.
The invention has the technical beneficial effects that:
(1) the invention utilizes alpha-Al 2 O 3 The crystal whisker has the characteristics of high specific strength, high specific modulus and stable high-temperature chemical property and is a single crystal short fiber, and the alpha-Al is made by adopting a suction filtration process 2 O 3 The whiskers are stacked in space to form a loose structure with high porosity. The sintered ceramic fiber is microscopically in a mesh structure similar to ceramic fiber and high in porosity, and the characteristics of high mechanical strength and high porosity are achieved.
(2) The invention utilizes the high activity and the adsorptivity of the nano-alumina particles to increase the contact area between the whiskers, improve the heat and mass transfer process in the sintering process, and improve the bonding strength of two kinds of alumina powder, thereby obtaining the porous ceramic.
(3) The invention realizes the preparation of the biscuit and the pore-forming by using a suction filtration method, has simple preparation process and low cost, and is easy for industrialized popularization.
Drawings
FIG. 1 shows Al prepared in example 1 2 O 3 SEM image of porous ceramic.
FIG. 2 shows Al prepared in example 2 2 O 3 SEM image of porous ceramic.
FIG. 3 shows Al prepared in example 3 2 O 3 SEM image of porous ceramic.
FIG. 4 shows Al prepared in example 4 2 O 3 SEM image of porous ceramic.
FIG. 5 shows Al prepared in example 5 2 O 3 SEM image of porous ceramic.
FIG. 6 shows Al prepared in examples 2, 5 and 6 2 O 3 XRD pattern of porous ceramic.
FIG. 7 is a graph showing the mechanical properties and porosity of the material under different slurry addition levels in the experiment of the present invention.
FIG. 8 is the variation curve of the mechanical property and porosity of the material at different sintering temperatures.
FIG. 9 is a graph of a sintering process during the manufacturing process of the present invention.
Detailed Description
The invention is further described with reference to the following figures and specific examples.
High-porosity Al 2 O 3 The preparation method of the porous ceramic comprises the following steps:
(1)α-Al 2 O 3 whiskers and nano-scale alpha-Al 2 O 3 The organic matter slurry of the powder is at least mixed according to the weight ratio of 1:1 or according to any proportion within the range of 1 to 6 in weight ratio, uniformly mixing with 70ml of deionized water to form suspension;
further, the average diameter of the alumina whiskers in the step (1) is 0.6 μm, and the average length is 9.2 μm; the inherent content of the alumina organic slurry was 76%.
The alumina organic matter slurry consists of two components of A, B, including SX-8317 as main component and transparent curing agent, and has main component of nanometer alumina powder and curing agent B as both of which are volatile, A, B components are mixed in the ratio of 1 to 1 before use, and the slurry has density of 2.6g/cm 3 The total content of the intrinsic substances at ordinary temperature was 76%.
Further, the mixing process of the suspension obtained in the step (1) further comprises the following steps:
mixing the alumina whisker and 70ml of deionized water, putting the mixture into an ultrasonic dispersion machine for ultrasonic mixing, and taking out the mixture after the mixture is fully dispersed until no whisker visible to naked eyes is agglomerated to obtain a turbid liquid. Adding the alumina organic matter slurry into the suspension, transferring the suspension into a planetary ball mill, and stirring to obtain the suspension in the step (1), and finally obtaining uniform suspension;
(2) in order to facilitate subsequent demoulding, a small amount of silicone grease is coated on the inner wall of the suction filtration device, then the uniform suspension obtained in the step (1) is transferred into the suction filtration device, and a vacuum pump is used for suction filtration of water to obtain a wet ceramic blank.
Further, the vacuumizing pressure of the vacuum pump in the step (2) is 100 mbar; after the filter paper is subjected to primary suction filtration, no obvious bubbles are generated, the green body above the filter paper is completely subjected to suction filtration, and the suction filtration time is about 12-15 min;
(3) placing the wet blank obtained in the step (2) in a drying oven, and drying at the constant temperature of 40 ℃ for 24 hours to obtain a biscuit;
(4) and (4) sintering the biscuit obtained in the step (3) at the sintering temperature of 1200-1400 ℃ to obtain the porous ceramic.
Further, in the sintering process in the step (4), the heating rate is 5 ℃/min.
Further, in the sintering process in the step (4), the heat preservation time at the sintering temperature is 360 min.
Further, in the cooling process in the step (4), the cooling rate is 5 ℃/min, and the furnace temperature is cooled along with the furnace after being reduced to 300 ℃.
Example 1
(1) Mixing 1g of alumina whisker and 70ml of deionized water, and putting the mixture into an ultrasonic dispersion machine for ultrasonic mixing to obtain suspension;
(2) mixing the suspension obtained in the step (1) with organic matter slurry of 1g of nano-scale alumina powder, transferring the mixture into a planetary ball mill, and carrying out ball milling and stirring for 5min at the speed of 400r/min to obtain uniform suspension;
(3) transferring the uniform suspension obtained in the step (2) into a suction filtration device, and performing suction filtration on water for 10-12min by using a vacuum pump at a vacuum pressure of 100mbar to obtain a ceramic wet blank;
(4) placing the wet blank obtained in the step (3) in a drying oven, and drying at the constant temperature of 40 ℃ for 24 hours to obtain a biscuit;
(5) placing the biscuit obtained in the step (4) in a box-type muffle sintering furnace, and carrying out heat preservation treatment for 360min at 1400 ℃ to obtain alpha-Al 2 O 3 A porous ceramic; the temperature rise rate of the box type muffle sintering furnace is 5 ℃/min, the temperature reduction rate is 5 ℃/min, and the furnace temperature is cooled along with the furnace after being reduced to 300 ℃.
(6) The porosity of the prepared porous ceramic sample is 90.31 percent, and the porous ceramic sample is resistant to pressureThe strength is 0.47MPa, and the density is 0.38g cm -3 The SEM image is shown in FIG. 1.
Example 2
(1) Mixing 1g of alumina whisker and 70ml of deionized water, and putting the mixture into an ultrasonic dispersion machine for ultrasonic mixing to obtain suspension;
(2) mixing the suspension obtained in the step (1) with 4g of organic matter slurry of nano-scale alumina powder, transferring the mixture into a planetary ball mill, and stirring the mixture for 5min at the speed of 400r/min to obtain uniform suspension;
(3) transferring the uniform suspension obtained in the step (2) into a suction filtration device, and performing suction filtration on water for 10-12min by using a vacuum pump at a vacuum pressure of 100mbar to obtain a ceramic wet blank;
(4) and (4) placing the wet blank obtained in the step (3) in a drying oven, keeping the temperature constant at 40 ℃, and drying for 24 hours to obtain a biscuit.
(5) Placing the biscuit obtained in the step (4) in a box-type muffle sintering furnace, and carrying out heat preservation treatment for 360min at 1400 ℃ to obtain alpha-Al 2 O 3 A porous ceramic; the temperature rise rate of the box type muffle sintering furnace is 5 ℃/min, the temperature reduction rate is 5 ℃/min, and the furnace temperature is cooled along with the furnace after being reduced to 300 ℃.
(6) The porosity of the prepared porous ceramic sample is 82.73%, the compressive strength is 4.48MPa, and the density is 0.69 g-cm -3 The SEM image is shown in FIG. 2.
Example 3
(1) Mixing 1g of alumina whisker and 70ml of deionized water, and putting the mixture into an ultrasonic dispersion machine for ultrasonic mixing to obtain suspension;
(2) and (2) mixing the suspension obtained in the step (1) with 6g of organic matter slurry of nano-scale alumina powder, transferring the mixture into a planetary ball mill, and stirring the mixture for 5min at the speed of 400r/min to obtain uniform suspension.
(3) Transferring the uniform suspension obtained in the step (2) into a suction filtration device, and performing suction filtration on water for 10-12min by using a vacuum pump at a vacuum pressure of 100mbar to obtain a ceramic wet blank;
(4) and (4) placing the wet blank obtained in the step (3) in a drying oven, keeping the temperature constant at 40 ℃, and drying for 24 hours to obtain a biscuit.
(5) Placing the biscuit obtained in the step (4)Performing heat preservation treatment for 360min at 1400 ℃ in a box-type muffle sintering furnace to obtain alpha-Al 2 O 3 A porous ceramic; the temperature rise rate of the box type muffle sintering furnace is 5 ℃/min, the temperature reduction rate is 5 ℃/min, and the furnace temperature is cooled along with the furnace after being reduced to 300 ℃.
(6) The porosity of the prepared porous ceramic sample is 77.83 percent, the compressive strength is 4.33MPa, and the density is 0.88g cm -3 The SEM image is shown in FIG. 3.
Example 4
(1) Mixing 1g of alumina whisker and 70ml of deionized water, and putting the mixture into an ultrasonic dispersion machine for ultrasonic mixing to obtain suspension;
(2) mixing the suspension obtained in the step (1) with 4g of organic matter slurry of nano-scale alumina powder, transferring the mixture into a planetary ball mill, and stirring the mixture for 5min at the speed of 400r/min to obtain uniform suspension;
(3) transferring the uniform suspension obtained in the step (2) into a suction filtration device, and performing suction filtration on water for 10-12min by using a vacuum pump at a vacuum pressure of 100mbar to obtain a ceramic wet blank;
(4) placing the wet blank obtained in the step (3) in a drying oven, and drying at the constant temperature of 40 ℃ for 24 hours to obtain a biscuit;
(5) placing the biscuit obtained in the step (4) in a box-type muffle sintering furnace, and carrying out heat preservation treatment for 360min at 1200 ℃ to obtain alpha-Al 2 O 3 A porous ceramic; the temperature rise rate of the box type muffle sintering furnace is 5 ℃/min, the temperature reduction rate is 5 ℃/min, and the furnace temperature is cooled along with the furnace after being reduced to 300 ℃.
(6) The porosity of the prepared porous ceramic sample is 86.61%, the compressive strength is 1.40MPa, and the density is 0.54g cm -3 The SEM image is shown in FIG. 4.
Example 5
(1) Mixing 1g of alumina whisker and 70ml of deionized water, and putting the mixture into an ultrasonic dispersion machine for ultrasonic mixing to obtain suspension;
(2) mixing the suspension obtained in the step (1) with 4g of organic matter slurry of nano-scale alumina powder, transferring the mixture into a planetary ball mill, and stirring the mixture for 5min at the speed of 400r/min to obtain uniform suspension;
(3) transferring the uniform suspension obtained in the step (2) into a suction filtration device, and performing suction filtration on water for 10-12min by using a vacuum pump at a vacuum pressure of 100mbar to obtain a ceramic wet blank;
(4) placing the wet blank obtained in the step (3) in a drying oven, and drying at the constant temperature of 40 ℃ for 24 hours to obtain a biscuit;
(5) placing the biscuit obtained in the step (4) in a box-type muffle sintering furnace, and carrying out heat preservation treatment for 360min at 1300 ℃ to obtain alpha-Al 2 O 3 A porous ceramic; the temperature rise rate of the box type muffle sintering furnace is 5 ℃/min, the temperature reduction rate is 5 ℃/min, and the furnace temperature is cooled along with the furnace after being reduced to 300 ℃.
(6) The porosity of the prepared porous ceramic sample is 84.88%, the compressive strength is 2.70MPa, and the density is 0.60g cm -3 The SEM image is shown in FIG. 5.
alpha-Al obtained at different sintering temperatures in examples 2, 4 and 5 2 O 3 The X-ray diffraction pattern of the porous ceramic is shown in FIG. 6.
The invention uses nano-grade alpha-Al 2 O 3 Slurry and alpha-Al 2 O 3 The whisker is used as a raw material, is mixed in different proportions and is prepared into the porous ceramic material with low density, high porosity and certain mechanical strength by adopting a suction filtration molding method. In the sintering process, the whiskers are mutually crossed and overlapped, alumina particles are adsorbed around the whiskers to carry out solid phase reaction to improve the strength, and the alpha-Al with high porosity is obtained after furnace cooling 2 O 3 A porous ceramic.
According to the result analysis of the SEM picture shown in fig. 1, the pore diameter of the porous material obtained in example 1 is about 5 μm, and the "arch bridge effect" between the whiskers can be clearly seen, and the whiskers are staggered with each other, and have a large number of pores, resulting in high porosity of the block; according to the result analysis of the SEM picture shown in fig. 2, in the porous material obtained in example 2, the nano alumina particles are significantly increased, the whiskers and the particles are well dispersed, and most of the particles are adsorbed at the junction of the whiskers to undergo self-sintering, thereby improving the mechanical strength of the bulk material; according to the analysis of the SEM picture results shown in fig. 3, in the porous material obtained in example 3, a phenomenon that a large number of nano alumina particles are agglomerated in the bulk is observed, and the agglomerated nano alumina particles gradually fill the space created by the stacking of whiskers, resulting in a decrease in the overall porosity of the material;
examples 1, 2 and 3 show that as the addition amount of the slurry containing nano alumina particles in the mixed raw material increases, the nano alumina particles are preferentially adsorbed to whiskers, and after the addition amount is excessive, the nano alumina particles are agglomerated and self-sintered, so that the porosity of the material is reduced;
according to the results of SEM pictures shown in fig. 4, in the porous material obtained in example 4, no degradation of the whiskers in the bulk, a small amount of agglomeration of the alumina particles, and a small amount of sintering at the intersections of the whiskers were observed; according to the results of SEM pictures shown in fig. 5, in the porous material obtained in example 5, it was observed that no significant deterioration of the whiskers in the bulk occurred, the whiskers were well dispersed with the alumina particles, and the sintering degree at the junctions of the whiskers was more sufficient;
example 2, example 5 and example 6 show that as the maximum sintering temperature of the alumina porous ceramic is increased, the dispersion condition of whiskers and particles in the ceramic is not obviously changed, the sintering process is more sufficient, and the mechanical strength is increased after sufficient mass transfer; when the sintering temperature reaches above 1400 ℃, the whiskers have a degradation phenomenon and tend to develop into isometric crystals.
According to alpha-Al shown in FIG. 6 2 O 3 The comparison of XRD patterns of the porous ceramics can clearly observe the alpha-Al of the standard card number 00-001-1243 2 O 3 The characteristic peaks of the three strong lines are respectively (104), (113) and (116), and 2 theta corresponds to 35.165 degrees, 43.473 degrees and 57.955 degrees respectively; the positions of the characteristic peaks of the samples, the whiskers and the bonding agent at all temperatures are quite consistent with the characteristic peak of the alumina with the standard card number of 00-001-1243, the peak positions are regular, the crystal structures and the components of the samples are the same, and the samples have stable crystal structures and no new phases in the sintering process.
The experimental data of the present invention shown in FIGS. 7, 8 and 9 show that Al is prepared according to the conventional method 2 O 3 Compared with porous ceramics, the invention has better technical effect, and adopts the formula (1:4) and the sintering temperature (1350℃)The porosity of the prepared porous ceramic sample is 82.73%, the compressive strength is 4.48MPa, and the density is 0.69g cm -3 ；
The thermal conductivity of the material obtained by LFA laser thermal conductivity meter detection is as low as 1.37-3.23W/m.K within the temperature range from room temperature to 1200 ℃, and the high porosity and sufficient mechanical strength of the material can be seen, so that the material has wide application prospects in the aspects of high-temperature heat preservation and high-temperature gas filtration.
The raw materials selected by the formula of the invention are nano alumina particles and alumina whiskers as raw materials; the high activity and strong adsorption of the nano alumina particles are utilized to promote the heat transfer and mass transfer processes in the sintering process of the alumina whiskers. The method not only fully utilizes the characteristics of the alumina whiskers as the single crystal short fibers to form a fluffy net structure in space, but also utilizes the nano alumina particles to solve the problems of small contact area between the alumina whiskers and poor bonding after sintering. Solves the problem that the prior art is difficult to obtain a loose net structure in the microstructure of the ceramic material; a fluffy structure with high porosity and superfine pores similar to a ceramic fiber membrane is obtained on the alumina ceramic material.
The high activity and strong adsorption of the nano alumina particles are utilized to promote the heat transfer and mass transfer processes in the sintering process of the alumina whiskers. Solves the problems of poor heat and mass transfer performance during sintering and low bonding strength between the whiskers after sintering caused by small contact area between the alumina whiskers.
The foregoing is only a preferred embodiment and description of the present invention, and it should be understood that various changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (8)

1. A preparation method of alumina porous ceramic with a similar ceramic fiber net structure inside is characterized by comprising the following steps:
(1) the organic slurry of the alpha-Al 2O3 whisker and the nano-scale alpha-Al 2O3 powder at least comprises the following components in percentage by weight of 1:1 or according to any proportion within the range of 1 to 6 in weight ratio, uniformly mixing with 70ml of deionized water to form stable suspension;
(2) transferring the suspension obtained in the step (1) into a suction filtration device, and performing suction filtration on water by using a vacuum pump to obtain a ceramic wet blank;
(3) drying the wet blank obtained in the step (2) to obtain a biscuit;
(4) sintering the biscuit obtained in the step (3) at the highest sintering temperature of 1200-1400 ℃ to obtain porous ceramic;
the average diameter of the alumina crystal whisker in the step (1) is 0.6 μm, and the average length is 9.2 μm; the solid content in the alumina organic slurry was 76%.
2. The method for preparing alumina porous ceramic with network structure similar to ceramic fiber according to claim 1, wherein the mixing process of the suspension obtained in step (1) further comprises the following steps:
mixing alumina whiskers with 70ml of deionized water, putting the mixture into an ultrasonic dispersion machine for ultrasonic mixing, and taking out the mixture after the mixture is fully dispersed until no whiskers visible to naked eyes agglomerate, so as to obtain a suspension; and (3) adding the alumina organic matter slurry into the suspension, transferring the suspension into a planetary ball mill, and stirring to obtain the uniform suspension finally obtained in the step (1).
3. The method for preparing alumina porous ceramic having a network structure similar to ceramic fiber according to claim 1, wherein the evacuation pressure of the vacuum pump in the step (2) is 100 mbar.
4. The method for preparing the alumina porous ceramic with the internal structure similar to the ceramic fiber net structure as the claim 1, wherein in the step (2), a little silicone grease is coated on the inner wall of the suction filtration device.
5. The method for preparing alumina porous ceramic with similar ceramic fiber net structure inside according to claim 1, wherein the drying in step (3) is carried out by drying at 40 ℃ for 24 hours using a drying oven.
6. The method for preparing alumina porous ceramic with internal structure similar to ceramic fiber net structure as claimed in claim 1, wherein the temperature rise rate in the sintering process of step (4) is 5 ℃/min.
7. The method for preparing alumina porous ceramic with similar ceramic fiber net structure inside according to claim 1, wherein the sintering temperature is kept for 360min during the sintering process of step (4).
8. The method for preparing the alumina porous ceramic with the internal structure similar to the ceramic fiber net structure as claimed in claim 1, wherein in the temperature reduction process of the step (4), the temperature reduction rate is 5 ℃/min, and the furnace temperature is reduced to 300 ℃ and then is cooled along with the furnace.
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